$ F = \left[\begin{array}{rrr}2 & 0 & 0 \\ 2 & 1 & 2 \\ 0 & 2 & 0\end{array}\right]$ What is $ F^{-1}$ ?
Answer: $ = \left[\begin{array}{rrr}\frac{1}{2} & 0 & 0 \\ 0 & 0 & \frac{1}{2} \\ -\frac{1}{2} & \frac{1}{2} & -\frac{1}{4}\end{array}\right]$